1. Field of the Invention
The present invention relates to a seat track apparatus, and more particularly to a seat track apparatus for vehicle seats.
2. Description of the Prior Art
In a conventional seat track apparatus for vehicle seats, for example, in FIGS. 1-3, an upper rail 13 which has a reverse U-cross-sectional configuration and is fixedly attached to a lower portion of a seat portion 11 of a seat 10, receives a lower rail 12 therein, which has U-cross-sectional configuration and is fixedly connected to a floor of a vehicle chamber. The upper rail 13 is movably connected to the lower rail 12 along the longitudinal direction and is supported on the lower rail 12 by rollers 14 for bearing at forward and rearward portions. The upper rail 13 is guided so as to move parallel to the lower rail 12 by a pair of ball bearings 15, 15 arranged at opposite sides of roller 14. In the above-mentioned apparatus, a clearance c exists longitudinally between upper faces of upper flanges 12a, 12a of the lower rail 12 and lower face of the upper rail 13 and furthermore the pair of ball bearings 15, 15 are supported by lower flanges 13a, 13a of the upper rail 13, so that when a large load is upwardly acted on the upper rail 13 as shown in FIG. 4, the lower flanges 13a, 13a of the upper rail 13 are bent downwardly and the upper rail 13 shifts in an upward direction and upper flanges 12a, 12a of the lower rail 12 are upwardly bent as shown in FIG. 5. As a result, the rearward portion of the upper rail 13 is in turn upwardly bent and deformed. Thus this conventional seat track apparatus is accompanied by drawbacks regarding the strength of the upper and lower rail 13, 12.